Tip/Suggestion:  Since this is not an accessor method, you can go after the tmp_dir property in the normal way (i.e. <code>self.tmp_dir m self['tmp_dir'] , etc.</code>.  This adds flexibility for a subclass to implement <code>get_tmp_dir(), set_tmp_dir(), del_tmp_dir()</code> accessor methods.  However, if they're not defined, default behavior is to just go after the dictionary value, so it works both ways.

What you have here is fine though, mostly just FYI.